Compact 433 MHz antenna for wireless smart system applications

Abstract

A compact, planar antenna operating at 433 MHz is proposed for wireless smart systems with dimensions of 51 × 28 mm 2 including a ground plane, and printed on a low-cost FR4 material. Significant size reduction is achieved using the variation of an inverted-F antenna configuration with a square-spiral section and rectangular patch element. Fine-tuning of the antenna's resonant frequency is possible using a small capacitive stub. Sensor and radio transceiver electronics can be accommodated above the ground plane. The measured results indicate a 10 dB return loss bandwidth of 4.5 MHz, and a peak realised gain of −13 dBi with omnidirectional radiation characteristics.Introduction: In recent years, wireless smart systems have rapidly emerged in areas such as healthcare and activity monitoring with applications in outpatient monitoring and the provision of in-home lifelines for the elderly [1, 2]. Wireless sensor motes operating in the 433 MHz industrial scientific and medical (ISM) band are a popular choice for low data rate applications and provide a good communication range due to reduced body absorption when compared to higher frequencies.Small and lightweight sensor realisations are key constraints for unobtrusive monitoring and an example of a 433 MHz sensor device is presented in [3] measuring 25 mm 2 in size excluding the antenna. A λ 0 /4 resonant antenna at 433 MHz would require dimensions of ∼170 mm excluding a ground plane. For the intended application, the goal is to realise a wrist-worn sensor with an area of 51 × 28 mm 2 . This size constraint means that a λ 0 /4 antenna is impractical and significant reduction of antenna dimensions is therefore necessary. It is well known however that decreasing the antenna size can negatively affect the efficiency, gain and bandwidth of the antenna [4]. Several small-sized 433 MHz antennas have been reported in the literature [5][6][7], but these antennas are too large in size for this application. A dual-band loop antenna configuration with dimensions very similar to those required is presented in [8] with a reported gain figure of −20 dBi at 433 MHz. In this Letter, an antenna structure is proposed that meets the required size constraints while also providing an acceptable figure for a peak realised gain of −13 dBi. The Letter discusses the design of the proposed antenna structure as well as size reduction methods. In addition, the simulated and measured results for the antenna impedance and radiation characteristics are presented and discussed.

Compact UHF/VHF Monopole Antennas for CubeSats Applications

“…To achieve a compact structure, different miniaturization techniques are preferred in this design. For the UHF monopole working at 398 MHz, meander-line technique [11][12] is implemented.The use of meander-line technique plays a role in reducing the antenna size. When the electromagnetic wave is fed into the antenna structure from the feed point, the current in the adjacent vertical branch of the curved polyline is in the opposite direction.…”

A High-Efficiency Compact Planar Antenna for ISM Wireless Systems

“…This novel electrically small antenna can be operated well without lumped elements for impedance matching as shown in Figure 1. Square-spiral antenna [8] 51 × 28 −13 Metal-shielding box antenna [7] 82 × 51 −4.3…”

“…This antenna is, however, still too large to be applicable in the compact wireless applications, that is, remote keyless entry systems. A very compact PCB antenna with dimensions of 51 × 28 mm 2 including the ground plane was presented in [8]. However, the significant size reduction was achieved at a cost of significant reduction of the antenna gain to −13 dBi.…”

One Ultra-Wideband Lumped-Element Loaded Antenna for Radio Instrument Measurement

“…It has been verified that capacitive loading keeps the radiation efficiency at 100%, that a combination of resistive and capacitive loading maintains the radiation efficiency between 40% and 60% (depending on the profile), and that resistive loading can in some cases reduce the radiation efficiency down to 30% [14][15][16][17][18]. However, research shows that resistive loading is the most effective one for suppressing late-time ringing, while capacitive loading (alone or in combination with resistive loading) still exhibits a relatively high level of ringing [19][20][21][22][23]. Furthermore, difficulties have also been shown in the practical implementation of nonlinear loading profiles (e.g., Wu-King) on planar structures such as bow-tie antennas.…”